Infiltration of meningeal macrophages into the Virchow–Robin space after ischemic stroke in rats: Correlation with activated PDGFR-β-positive adventitial fibroblasts

Abstract

Macrophages play a crucial role in wound healing and fibrosis progression after brain injury. However, a detailed analysis of their initial infiltration and interaction with fibroblasts is yet to be conducted. This study aimed to investigate the possible route for migration of meningeal macrophages into the ischemic brain and whether these macrophages closely interact with neighboring platelet-derived growth factor beta receptor (PDGFR-β)-positive adventitial fibroblasts during this process. A rat model of ischemic stroke induced by middle cerebral artery occlusion (MCAO) was developed. In sham-operated rats, CD206-positive meningeal macrophages were confined to the leptomeninges and the perivascular spaces, and they were not found in the cortical parenchyma. In MCAO rats, the number of CD206-positive meningeal macrophages increased both at the leptomeninges and along the vessels penetrating the cortex 1 day after reperfusion and increased progressively in the extravascular area of the cortical parenchyma by 3 days. Immunoelectron microscopy and correlative light and electron microscopy showed that in the ischemic brain, macrophages were frequently located in the Virchow–Robin space around the penetrating arterioles and ascending venules at the pial surface. This was identified by cells expressing PDGFR-β, a novel biomarker of leptomeningeal cells. Macrophages within penetrating vessels were localized in the perivascular space between smooth muscle cells and PDGFR-β-positive adventitial fibroblasts. In addition, these PDGFR-β-positive fibroblasts showed morphological and molecular characteristics similar to those of leptomeningeal cells: they had large euchromatic nuclei with prominent nucleoli and well-developed rough endoplasmic reticulum; expressed nestin, vimentin, and type I collagen; and were frequently surrounded by collagen fibrils, indicating active collagen synthesis. In conclusion, the perivascular Virchow–Robin space surrounding the penetrating vessels could be an entry route of meningeal macrophages from the subarachnoid space into the ischemic cortical parenchyma, implying that activated PDGFR-β-positive adventitial fibroblasts could be involved in this process.

Leptomeningeal Neural Organoid (LMNO) Fusions as Models to Study Meninges-Brain Signaling

“…The meninges contain tissue-resident yolk-sac derived macrophages called border associated macrophages (BAMs) that play an important role in immunological surveillance and response to infection and injury 18,19 . BAMs appear in the meninges embryonically persisting through adulthood and are identified by the markers CD206 (also known as mannose receptor C-type 1 (MRC1)) and lymphatic vessel endothelial hyaluronan receptor 1 (LYVE1).…”

“…We previously showed that some meningeal fibroblast layer specific markers (e.g., S100a6, CRABP2) are shared between fetal mouse and human meninges 15 . To further test this, we used published single nuclear RNA sequencing data sets from early embryonic (human gestational week 6-10) and later fetal (gestational week [16][17][18][19][20][21][22][23][24][25] human brain development to identify cell clusters that are representative of putative meningeal mesenchymal/fibroblast, meningeal macrophage, and vascular cells (Fig. 1D, E).…”

Brain perivascular macrophages: current understanding and future prospects

“… 38 One study of a middle cerebral artery occlusion (MCAO) rat model demonstrated that the number of CD206 + macrophages increased significantly both at the leptomeninges (leptomeningeal macrophages) and along the vessels penetrating the cortex (PVMs). 106 , 122 Another study reported that the population of CD163 + brain PVMs was maintained, while their gene expression profile changed dramatically. 39 Additionally, CD163 + brain PVMs could secrete VEGF, which led to increased vascular permeability and leucocyte migration into the brain.…”

Immune compartments at the brain’s borders in health and neurovascular diseases

“…Another study in rats also examining CD163 + cells suggested this increase began not earlier than 24 h after ischemia [ 80 ]. Similarly, using CD206 as a BAM marker, it was found that BAM increased in meninges and the perivascular space along penetrating vessels from day 1 to 3 after transient MCA occlusion in rats; however the study suggested migration from the meninges as the main mechanism for this increase [ 81 ]. Interestingly, a study of six human cases with a history of MCA infarction found increased MHC class II positive PVM in the spinal cord weeks to several years after the ischemic event.…”